(57) The present invention relates to the preparation of aminoalkyl p-hydroxyphenyl ketones. Certain of these ketones are well known as important intermediates in the production of compounds having pharmaceutical activity, for example octopamine or synephrine.
The known Houben-Hoesch reaction is a variation of the Friedel-Crafts reaction and involves the condensation of a phenolic substrate with a nitrile in the presence of a Lewis acid catalyst to give a hydroxy-aryl ketone.
It is an object of the invention to provide a new or improved process for the manufacture of aminoalkyl p-hydroxyphenyl ketones.
According to the invention, there is provided a process for the preparation of an aminoalkyl p-hydroxyphenyl ketone comprising reacting phenol with a nitrile, in the presence of a Lewis acid catalyst, to cause condensation thereof, the process being characterised in that the reaction is carried out in a medium comprising a nitroalkane solvent for the reactants.
A preferred but non-limiting feature of the invention is the productiqn of 2'amino-4-hydroxyacetophenones.
The present invention is based on the surprising discovery that nitroalkanes are unexpectedly much better solvents for this reaction, being less toxic, giving a better yield and also ensuring a homogeneous reaction medium. The nitroalkanes may also be diluted with a halogenated hydrocarbon solvent, which acts as an inert diluent, thus reducing the amount of nitroalkane used, and making the reaction less hazardous.